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Specifying "ISO 20457 Tg5" on a drawing is not enough to be legally enforceable. According to technical guides , a complete specification must include: : e.g., TG5.
: Whether using a CMM (Coordinate Measuring Machine) or a manual fixture. Why Choose TG5?
: Coarse to very coarse (e.g., packaging or parts with high, unpredictable shrinkage). Key Components of an ISO 20457 Callout Iso 20457 Tg5
: The environmental state (typically 23°C and 50% relative humidity) at which the part must be measured. Datum Scheme : The reference points used for measurement.
ISO 20457 , which replaced older standards like DIN 16901 and DIN 16742, defines the geometrical and dimensional tolerances for plastic molded parts. Unlike metal machining, plastic molding must account for unique variables such as material shrinkage, thermal expansion, and moisture absorption. Understanding the TG5 Classification Specifying "ISO 20457 Tg5" on a drawing is
refers to a specific "Tolerance Group" (TG) within the international standard for plastic molded parts. Specifically, TG5 is the baseline standard precision grade used for general-purpose industrial applications, such as housing parts and enclosures. What is ISO 20457?
: Standard Baseline Precision. This is the "default" for technical parts where fit and function are important but not microscopic. Why Choose TG5
Using balances cost and quality. Tighter groups (TG1–TG4) significantly increase tooling costs and scrap rates because they require narrower process windows. TG5 provides sufficient accuracy for: Consumer electronics housings. Automotive interior trim. Medical device enclosures. Summary Table: ISO 20457 Tolerance Hierarchy Accuracy Level Typical Application Extreme Precision Optical components, micro-fluidics High Precision Gears, functional mechanical parts TG5 Standard Precision Industrial housings, technical components Packaging, disposable goods
: Extreme precision (expensive and difficult to maintain). TG4 : High precision (e.g., gears or precision wheels).
For more detailed engineering data, you can view the official abstract on the ISO website or check the DIN ISO 20457 comprehensive guide .
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